A. Field of the Invention
The invention generally concerns resilient foams, and more specifically to resilient foams made from derivatized polyanionic polysaccharides. The resilient foams are capable of forming a thixotropic hydrogel when contacted with water, blood, wound exudate, etc.
B. Description of Related Art
Medical materials (for example, gels or splints) are intended for use in a variety of surgical procedures (for example, nasal and/or sinus surgery) and/or wound treatments to control bleeding, edema, and prevent adhesions between adjacent soft tissues structures. In recent years there have been numerous efforts to make materials that minimize bleeding and edema that dissolve, biologically degrade, or fragment after performing their function. Examples of some current medical materials are Stammberger Sinu-Foam™ (ArthroCare, Austin, Tex.), NasoPore® (Polyganics, The Netherlands), XeroGel® (Cogent Therapeutics, Haywood, Calif.), SepraGel® (Genzyme, Corp., Cambridge, Mass.), and MeroGel® and MeroPack®, (Medtronic, Jacksonville, Fla.). These materials are foams and/or gels that are malleable, however, they tend not to hold their shape or provide sufficient mechanical force to immobilize soft tissue, for example, nasal structures. Some of these materials must be stored under refrigeration and/or packaged in vacuum packs to inhibit thermal and oxidative degradation of the foam and/or gel. Many of the foamed materials must be hydrated during use to expand the foam, however, many of the materials fail to expand to a size sufficient to fill the cavity and/or provide sufficient mechanical strength to immobilize or support soft tissue. These materials and other current materials are made from polyurethanes and/or cross-linked various derivatives of polyanionic polysaccharides. Bioresorbable gels and stents are also described in U.S. Pat. No. 8,313,762, and U.S. Patent Application Publication No. 2003/0187381.
The problems associated with the current materials are numerous. First, the materials (for example, gels) serve only as a barrier or dressing and cannot be used to separate tissue. Second, many of the materials fragment or remain in the cavity or wound, and must be physically removed during the healing process. Such removal can aggravate the wound. Third, many of the methods to make the materials involve cross-linking processes, which can add several steps and/or expense to the production of the materials. Fourth, many of the materials must be irradiated or further processed to cause chain scission of the cross-linked compounds to promote degradation of the materials.